It is fairly common practice to combine a packet of cigarettes with a coupon, which is normally enclosed inside the packet with the group of cigarettes. The coupon may be either the same size as or larger than the packet of cigarettes; in which latter case, it is folded for insertion inside the packet.
A known packing machine for producing packets of cigarettes with folded coupons comprises a conveyor for feeding a number of seats, each containing a respective group of cigarettes, along a packing path. The packing path extends through a feed station where a wheel, comprising a number of gripping heads, extracts the folded coupons one at a time from the bottom of a stack housed inside a store, and feeds each folded coupon to a respective seat on a packing conveyor, together with the corresponding group of cigarettes.
Various tests show known packing machines of the type described above to function satisfactorily at relatively low speed (up to 4-5 packets of cigarettes a second) but poorly at high speed (over 7-8 packets of cigarettes a second) on account of the fairly long time required to remove a folded coupon correctly from the bottom of a stack of folded coupons.
Packing machines have therefore been proposed, in which, at the coupon feed station, a flat strip of preprinted coupons is unwound off a reel and cut into individual coupons by a cutting device; each coupon is fed to a folding unit by which it is folded; and a transfer device receives each folded coupon from the folding unit, and feeds the folded coupon to a respective seat on a packing conveyor, together with the corresponding group of cigarettes.
One example of a cigarette packing machine with an on-line coupon-folding feature is described in Patent Application WO-2004003726-A1. More specifically, the packing machine comprises a roller folding unit or so-called “buckle folder” in turn comprising a succession of folding stations, each for making one fold in the coupons, and each having two counter-rotating rollers and a locating member. In actual use, a coupon is received from a folding station so as to rest on the two counter-rotating rollers, with one end of the coupon resting against the locating member. At this point, an intermediate portion of the coupon is gradually engaged by the counter-rotating rollers, so that the coupon is fed between the counter-rotating rollers and so folded.
Another example of a “buckle folder” roller folding unit is described in Patent Application EP-0522408-A1.
“Buckle folder” roller folding units have numerous advantages: they are compact, cheap and easy to produce, and can operate at high speed. On the other hand, good-quality folding tends to be restricted to a small range of operating speeds. That is, a “buckle folder” roller folding unit only operates well at substantially constant operating speed; which limitation poses serious problems on a cigarette packing machine, which is subject to numerous changes in speed to adapt to the operating conditions of the automatic (cigarette manufacturing, cellophaning, and cartoning) machines to which it is connected, as well as for cleaning, adjustment, maintenance and format changes.